Display omitted •WO3/WS2 nanocomposites were successfully synthesized using facile hydrothermal method and subsequent annealing technique.•The gas sensing performance of WS2 and WO3/WS2 nanocomposites were investigated and shows excellent selectivity towards NO2.•WA-600 sensor showed a maximum response of 123% for 10 ppm NO2 with short response/recovery time of 11 s/ 163 s at RT.•The DFT calculations were performed to study the interfacial charge transfer between WO3/WS2 nanocomposite and gas molecules.•Gas sensing mechanism of WO3/WS2 nanocomposites were discussed. In this article, we synthesized WO3/WS2 nanocomposites by facile hydrothermal synthesis followed by thermal annealing treatment and analysed its gas sensing properties. The thermal annealing process was carried out in different temperatures from 400 ℃ to 600 ℃ to form WO3/WS2 nanocomposite. During the thermal annealing process, the hydrothermally synthesized pure WS2 nanosheets undergo partial oxidation constructing WO3 on the surface developing active heterojunctions leading to increment in the sensing performance. The fabricated WO3/WS2 samples showed superior sensitivity and selectivity towards NO2 gas molecules. The pristine WS2 nanosheets showed a response of 26% towards 10 ppm of NO2 gas with a response and recovery time of 13 s /18 s, whereas WO3/WS2 nanocomposite prepared by annealing at 600 ℃ showed a maximum response of around 123% with a short response time of 11 s and recovery time of 163 s. The DFT calculations were performed to understand the gas sensing performance and interfacial charge transfer between the WO3/WS2 nanocomposite and gas molecules. Therefore, this study demonstrates that the indigenous heterojunctions contribute extensively to improving the gas detection capabilities of WO3/WS2 nanocomposites at room temperature.